Calculation of transient current in transformers

The paper describes two general methods of calculating inrush currents in single-phase transformers, allowing for the effects of magnetic hysteresis. One method is to use a normalised representation of the magnetic characteristic. A numerical solution to the circuit equations is carried out, but, because the equations are dimensionless, the number of independent parameters is reduced from seven to three. This makes it possible to carry out a general study, with the results presented in the form of charts. The charts can then be scaled to obtain inrush current values for particular cases. The other method is based on a simple, yet accurate, modelling of magnetisation curves using a hyperbolic expression. In this case an algebraic solution of the circuit equations is obtained. Comparisons are included between experimental and calculated results.